According to the background art, it is known to acquire different views of a same scene with a plenoptic camera, also called light-field camera. FIG. 1 illustrates such a plenoptic camera 1 according to prior art. The plenoptic camera 1 is composed of a lens arrangement associated with a photosensor array 13, also called image sensor array 13. The photosensor array 13 comprises a large number m of photosensors 131, 132, 133 to 1m arranged in the form of a grid of X columns and Y lines, m corresponding to X time Y. A color filter array (CFA) 12 is arranged on the photosensor array 13. The CFA 12 typically arranges RGB (Red, Green and Blue) color filters on the photosensor array, the RGB arrangement taking for the example the form of a Bayer filter mosaic. Typically, one color filter (red, green or blue filter) is associated with one photosensor according to a predetermined pattern, which comprises 50% green, 25% red and 25% blue in the example of a Bayer filter, such a pattern being also called RGBG, GRGB or RGGB pattern. The lens arrangement comprises a primary lens 10, also called main lens, and a lenslet array 11, which comprises a plurality of n microlenses 111, 112, 1n, n being a positive integer greater than or equal to 2. The microlenses 111, 112, 1n are arranged in such a way as to be optically each associated with a plurality of photosensors. The number of photosensors optically associated with one microlens corresponds to the number of views of the scene acquired with the plenoptic camera 1. The photosensors associated with a given microlens form a microlens micro-image. To obtain the different views, the raw image (i.e. the color sensor data acquired with the photosensor array 13) is demosaiced and de-multiplexed. The demosaicing enables to recover a full color raw image, i.e. to recover full color information (for example RGB information, RGB standing for “Red”, “Green” and “Blue”) for the pixels of the raw image while the raw image acquired with the plenoptic image associates only one color component (R, G or B for example) with each pixel. The demultiplexing performed after the demosaicing enables to recover the different views of the scene, i.e. to group the pixels of the demosaiced raw image according to the view they belong to.
To recover the different views of the scene, it is necessary to calibrate the raw image acquired with the plenoptic camera. The main goal of this calibration is to identify centre point locations of each microlens micro-image formed on the photosensor array of the plenoptic camera. Due to various complications, the process pertaining to the identification of the center point location is plagued by various issues leading to mismatches between the estimated centers all over the photosensor array with the single location of the main lens sub-aperture which is supposed to be optically conjugated with those central pixels. If the photosensor array is provided with a Bayer type Color Filter Array (CFA), it impacts even more the precision of the estimation. If a global optimization is used to estimate the centers, such an optimization typically cannot take into account fabrication dispersion of individual microlenses in size and relative positions in the lenslet array. Moreover there is an ambiguity in the estimation of the center if the estimated position falls in the vicinity of the border between some pixels/photosensors: the nearest integer rounding to select the right pixel has a great probability to select a pixel which is not the central pixel of the micro-image.
Moreover, each time the main lens has undergone a change, either in zooming or in focalization, the micro-image centers have to be estimated again. For that reason, a flat white picture with the same lens settings has to be taken and from that image a least square optimization method used to retrieve the parameters needed to demultiplex the views. This creates an inconvenience because it is not very handy to calibrate the system each time the main lens has been tweaked for a snapshot. If the system is also video capable, this means also that zooming while filming is also prohibited.